Check her gums (I learned about this working for the vet). If they are white or very pale - call the vet. Rosey gums - could be multiple of things: gas, stomach acid, worms, food, ate something other than food, etc...
I hope she feels better soon.
Nutra-cal is a good thing to use until you know what it is.
P.S. Is she eatting grass = upset stomach.
T.